Ion bombardment is often used as a source of activation energy for chemical and physical processes in etch and chemical vapor deposition (CVD) processes for processing a semiconductor workpiece, for example, a wafer. Currently, wafer biasing technology uses radio frequency (RF) biasing techniques. These RF techniques generally use single frequency RF biasing to accelerate ions to be implanted into a wafer, which results in a fairly well known distribution of ion energy across the wafer. However, the density of ions at a particular ion energy (eV) is always distributed in well-known quantities, and the distribution is not tunable using RF biasing. Optimization of the etching process by careful control of the population of ions at a given ion energy is currently not possible, and the effect of different ion energies on process results is not known in detail.
Therefore, the inventors have provided a system that enables processing chambers to be tunable in order to tailor ion energy to independently control the maximum ion energy and the distribution of low and medium ion energies, or in other words, a system for tunable workpiece biasing in a plasma reactor.